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Emotiva CMX-2 "AC line filter with DC offset eliminator" - seeking opinions/reviews

Breezy

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I've just finished reading an amazing "audiophile fuitloopery" compilation thread on another forum, so I'm having a difficult time looking at products that don't quite do the conventional stuff and not feel skeptical. In my search for where the slight electrical hum comes about from the main transformer in my main AV receiver, I've stumbled upon this product:

Emotiva CMX-2
https://emotiva.com/products/cmx-2

Amazon reviews seem to be generally positive and claim that this filter helps with transformer hum and such. $130 is not cheap for just 2 sockets, and I have no idea if there are competitive products in this price range. It would seem like these would be sold all over the internet with many competing models to "solve" the "DC offset" issue.

What's the Audio Science conclusion on this product? Am I looking at the wrong solution to my problem?

(P.S.: no, I can't rewire my apartment. I wish I could, but it's difficult enough to get a licenced electrician to visit around here--all seem overloaded with contracts far in advance, and it also will cost prohibitively much).
 

RayDunzl

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Breezy

Breezy

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When do you hear it?

So far when the receiver's main transformer is powered on. So either in standby with HDMI passthrough enabled or just turned on and not doing anything. I've measured power consumption, and it's using about 29-30W doing that just sitting there, getting a bit warm too. I can feel slight vibration in addition to the hum when I place my hand over the top grille. The receiver is Pioneer VSX-532, for reference.

If I disable HDMI passthrough, it properly goes to low power sleep with around 0.5W energy consumption. No more buzz/hum. From what I've read, there's a secondary transformer just on to power the low power state standby mode, to enable operation via remote. As soon as I turn it back on from sleep mode though, the transformer hum comes back. I hear it from about 2 feet away in a Very quiet room.
 

bigx5murf

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I have a low hiss from my anthem preamp, that I've never been able to track down the cause. I've even met 2 owners of the same device locally and confirmed theirs do the same thing. I've tried a monster power conditioner, a panamax power conditioner, a large APC UPS, tripp-lite UPS, and tripp-lite surge protector. I also converted all my fluorescent lights to direct line LED. All with no change. It's only noticeable with nothing playing, and my ear inches from the tweeters, so I decided to just live with it.
 
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Breezy

Breezy

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I mean even at $110 warehouse deals it's not a cheap thing to get, but I'm considering it to try it out. Just curious if the engineering reasoning behind it is sound and whether there are more budget-friendly options. I don't know if all "power conditioners" are created equal, so to speak. My projector and AV receiver are plugged into a cyberpower battery backup power strip (for safe shut down for the projector, to make sure its CFL bulb is properly cooled by a fan in case of power outage). This Cyberpower unit has "power conditioning" listed as a feature, but it doesn't say anything about DC offset. I think what it means rather is that it tries to provide more constant voltage level in case of brown-outs or surges. The hum remains whether I plug the receiver into Battery+Surge outlet, Surge, or just straight into the wall bypassing the battery back-up strip.
 

RayDunzl

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Without an isolating transformer, a minor DC Offset is stopped by using diodes in the primary:

Maybe something like this in-line with whatever else before the power supply of the gear:

1544826613489.png


Someone more knowledgeable on the subject can correct/enhance this simplistic drawing.


Some (looks like) visible diodes near the input of the Emotiva:

1544826766832.png


Disclaimer: I have an isolation transformer, the power transformer hums coming after it are reduced. I can still hear them if I use a stethoscope. Before, one amplifier made noises sometimes audible across the room. The isolating transformer doesn't hum, so, ???
 
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bigx5murf

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IME, I wouldn't bother, the device I'm having similar issues with retailed for over $3k. I've verified the same model device in other people's homes have the same issue. I've verified my large collection of similar devices don't have the issue in my own house. I forgot to mention, I've verified the issue is still present even when running off battery power on UPS. How bad is your hum? Can you live with it? Is the device still under warranty?
 
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Breezy

Breezy

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That's interesting, you'd think AV receiver manufacturers would include some extra diodes. The transformer hum in AV receivers seems to be a non-uncommonly discussed topic, based on my google search.
 
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Breezy

Breezy

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IME, I wouldn't bother, the device I'm having similar issues with retailed for over $3k. I've verified the same model device in other people's homes have the same issue. I've verified my large collection of similar devices don't have the issue in my own house. I forgot to mention, I've verified the issue is still present even when running off battery power on UPS. How bad is your hum? Can you live with it? Is the device still under warranty?

It's not loud at all--the speakers will easily drown out that faint sound once something is playing through them, it's just a bit disconcerting to me to hear it and feel the slight vibration when I put my hand over the top ventilation grill. If I have HDMI passthrough enabled, it's not great to think about the receiver sitting there getting warm and vibrating all day long, so I will just keep that option disabled. Not under warranty, got it used from amazon, and it works well. Was not an expensive investment.
 

restorer-john

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DC offset is an issue just about everywhere it would seem. Toroidal transformers are most susceptible.

You can easily build your own. Here's an article and practical schematic:

http://sound.whsites.net/articles/xfmr-dc.htm
 
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Breezy

Breezy

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DC offset is an issue just about everywhere it would seem. Toroidal transformers are most susceptible.

You can easily build your own. Here's an article and practical schematic:

http://sound.whsites.net/articles/xfmr-dc.htm

Very interesting, thank you for the link. I've found these noteworthy to explore further for my case:

"Most of the time, the DC offset is transient - it appears for a short while, then goes away again. When it is there, toroidal transformers may complain loudly, by making growling or buzzing noises."

This is not what I experience with my AV receiver, so maybe my issue is not exactly the same. What I hear is a constant and consistent hum of the same pitch/frequency/amplitude. Nothing like sudden buzzing that comes and goes if an appliance is turned on or off.

"It's also worth noting that DC is usually not a problem with toroidal transformers of 300VA or less. "

Not sure what mine is rated for, but it's supposed to supply enough nominal power of 80W/channel for 8Ohm speakers. Only using under 30W from the wall when sitting in idle mode and humming away, not processing any signals.
 

RayDunzl

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Not sure what mine is rated for

VSX-532 5.1-Channel AV Receiver
Estimated Power Consumption/Network Standby off 210 W/0.35 W
 

restorer-john

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Some (looks like) visible diodes near the input of the Emotiva:

Those diodes are just 1A style like 1N4001-7 and most likely for reverse polarity protection for the LED indicators.

The four high current diodes are no doubt mounted on the opposite side of the board in the middle- note the 8 solder pigtails and the high current paths on the PCB. Capacitor values appear to be 470uF connected as per the classic DC blocking schematic I linked to. (10x less value however)
 
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Breezy

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I don't know if these are useful at all, but I've tried to take some photographs through the top grill of the AV receiver. It's much easier to see the components in person when shifting perspective slightly back and forth, but I've attempted to get some detail by getting the lens close to defocus the top. There are 2 huge capacitors. The main transformer is to the left of the capacitors: a big rectangular chunk of what looks like steel-colored thin wire wound over something rectangular. I can see more typical copper solenoids coming out of it from the front under that cream colored large connector.

Imgur album: (direct link for large sizes)
 

AnalogSteph

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Not sure what mine is rated for, but it's supposed to supply enough nominal power of 80W/channel for 8Ohm speakers. Only using under 30W from the wall when sitting in idle mode and humming away, not processing any signals.
I wonder how they're doing it with traditional AB amps - my old 3x 85 W + 2x 30 W ProLogic job draws about 80 W in idle if memory serves. Traditional 80-100 Wpc stereo amps tend to draw around 40-50 W.

I wouldn't call 6800 µF filter caps "huge" - it's what you get in this class, but you'll find ones just as large in a stereo amp of similar power rating. Samwha caps... not exactly premium grade, but then this is a rather inexpensive AVR, too. You get what you pay for.

It's a traditional EI core transformer. If it hums all the time, chances are it's got a screw loose ;), or QC slipped and you got a bum transformer. (I've had to tighten up the transformer mounting screws on my old beast once or twice to quiet down hum. It has never been dead silent but certainly acceptable. The most drastic case I've ever had was an old 13.8 V / 10 A DC supply where it turned out one of the bolts holding the transformer laminations together had come loose. That thing made quite the racket. After tightening up, only a very faint hum remained.) As you can see, these things are coated to stop things from vibrating. If you were near an industrial area with crappy mains, chances are hum levels would vary depending on daytime and what kind of machinery is being operated.
 
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Breezy

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As long as I can deal with the fairly quiet hum, it's not much of a safety issue, right? Or shortening the lifespan of components? Would something like that Emotiva strip make a difference?

P.S.: reading about EI transformers, interesting summary:
https://www.soundstage.com/maxdb/maxdb071998.htm

Though this person says you can't have an EI transformer in an AV receiver (multi-channel amplifier) unless it has expensive shielding (this receiver has nominal price of $280--I doubt that counts as "expensive")

"Aim the EI-frame transformer so that the core points towards the audio signal processing and so that the "bells" point to the sides and the radiated magnetic field won’t bother the audio circuits inside the amp. But putting an EI-frame in a tightly packed multi-channel amp or receiver is just about impossible...there just isn’t enough room to stay away from the radiated magnetic field. In those applications, you will almost always find toroidal power transformers. You can jam a toroid right into the middle of five amplification channels and have no problems from magnetic fields. Magnetic shielding for an EI-frame transformer is also possible, but it tends to be expensive and heavy. "

But then the article is 20 years old. Maybe engineering side of things has evolved to compensate.

P.S.: just to reiterate: the hum from my receiver is VERY quiet. My ear must be within 2 feet of it in a very quiet room to pick up the hum, and then it's quite faint. Only moving within 1 foot of the transformer do I hear definite hum. And putting my hand over the casing I feel some low vibration and warmth. Because my living room gets so quiet, I'm able to hear the hum, as I read on a couch near where I placed the receiver--that's how I first noticed the hum. It does sound much like a relatively quiet hum of an LED or CFL light bulb would.
 
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AnalogSteph

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My ear must be within 2 feet of it in a very quiet room to pick up the hum, and then it's quite faint. Only moving within 1 foot of the transformer do I hear definite hum.
Sounds normal to me. Keep in mind the transformer is effectively mounted to a big resonator (the case). If you're that picky, think about some options for elastic mounting.
 
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Breezy

Breezy

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I think I can live with it. I was more concerned it was bad and inefficient for the transformer and other components and general safety. If it's normal, then since I don't have HDMI pass-through enabled anymore, I won't hear the faint hum with speakers playing music / soundtracks from movies, so no big deal.
 

Kal Rubinson

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I have one of these and I got it in the hope that it would cure a hum in an old Paradigm subwoofer. It did not but that is because the hum was internal to the sub (defective power transformer). Since I have it as an independent filter/power strip, I use it still but there is nothing it needs to cure.
 

yodog

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I have one of these and I got it in the hope that it would cure a hum in an old Paradigm subwoofer. It did not but that is because the hum was internal to the sub (defective power transformer). Since I have it as an independent filter/power strip, I use it still but there is nothing it needs to cure.

Would this also be suitable to use to power my cable internet modem and router?
 
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